Whether you plan on visiting multiple cities on your Spanish vacation, or just one, it is best to plan ahead for all aspects of your vacation, including airfair, hotels, transportation, and of course entertainment. It is also extremely important to know the holidays in Spain, and even the customs 
of cities during those holidays. If you don't you can find that many of the businesses and local attractions are closed for days or even weeks at at time!
International Airline Carriers
In our experience, we've found several comfortable airlines to travel with that are still inexpensive and sometimes the have the lowest rate. The airlines that I would recommend are British Airways being the first choice, Air France being the second choice, or KLM as the third.
Traveling Within Spain
Traveling inside of Spain is much different than it is in the United States. Rental cars cost about double the price in Spain. Last time we took a rental car for a 5 day trip it was close to $100 per day. Avis, Hertz and most of the major car rental agencies have locations throughout Spain. If you make reservations in advance you may get lucky and get a reduced rate.
In addition to the rental rates, there are also toll roads in Catalunya which you will run into starting near Valencia and going all the way up to Barcelona. These tolls are $50-70 to drive from the Valencia area up through Barcelona, so be prepared. Driving in the Spanish countryside is an exciting and adventurous, but we just want you to know that it is not the most economical way to travel.
The train system is the most inexpensive way to get from one city to the next in Spain. Depending on the time of the year and location, they may be crowded and not as comfortable as you might like. Also, there are two different types of trains in Spain. The high speed trains will get you there quickly, but the slower trains can take 50% longer than driving by car.
Air travel is very inexpensive within Spain. A roundtrip ticket can be found on SpanAir or Iberia for $75-$150 to most parts of Spain. The mass transit system (busses, trains, subway) can usually get you to the airport economically, but the fastest way is by taxi.
Hotels in Spain
Just like any vacation you take, you should make sure your hotel is close enough to the sight seeing locations you want to visit, or at least near the local transportation. You can see many of the hotels on Expedia.com or even on Priceline.com. But beware of some of the ratings on hotels. Many of the hotels are older and may not be what you would expect from a 4-5 star hotel. So read up on the hotel and area you are visiting first.
Entertainment Throughout Spain
Make sure to research the specialties of the city that you are planning on visiting in Spain. Whether it is a flamenco show in the south or artwork in Barcelona, get a feel for what is available before visiting. You'll also want to leave plenty of time for sampling the local food and sangria in the many fine restaurants.
